Non-invasive blood pressure monitor

ABSTRACT

A non-invasive, non-occluding pressure transducer for monitoring subcutaneous blood pressure, which can be worn for extended periods of time without physical discomfort, for physiological, psychological and psychiatric evaluation, and for clinical procedures and surgical monitoring and truth-verification polygraph applications, having suitable frequency response characteristics for high-fidelity recordation of subcutaneous blood pressure changes.

SUMMARY OF THE INVENTION

The gist of this invention lies in a pressure transducer for monitoringsubcutaneous blood pressure, which is applied directly to the body orappendage of a subject, comprising a thin flat diaphragm which isflush-mounted with rigidly mounted edges fixity in the surface of aplate having a contour which conforms to the natural curve of the bodyor appendage of the subject, and which contoured plate is held againstthe subject's skin at an adjustable and predetermined bearing pressureby an adjustable-length strap which does not occlude the subject'sveins. Subcutaneous blood pressure applied to the contact face of saiddiaphragm develops mechanical strain in the back face of the same whichis sensed by electrical strain gages mounted on the back face thereof.The change in electrical resistance of these strain gages due to thismechanical strain immposed by said pressure operates conventionalelectrical monitoring and amplification circuitry and recordingapparatus.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan of the dry blood pressure tansducer of thisinvention having a diaphragm mounted in a substrate for attachment tothe finer or thum of the right or left hand.

FIG. 2 shows a side view of the same.

FIG. 3 shwos a blow-up plan view of the contact face of the same.

FIG. 4 shws a cross-sectional view along line 4--4 of FIG. 3.

FIG. 5 shows a block diagram of a system utilizing the subjecttransducer for monitoring blood pressure.l

FIG. 6 shows the electrical circuit diagram for the transducer.

FIG. 7 shows a cross-sectional side view of one typical placement of thetransducer with the dry skin as a sole coupling means.

FIG. 8 shows a cross-sectional side view of another placement thereof.

FIG. 9 shows a cross-sectional side view of still another placementthereof.

FIG. 10 shows end views of FIGS. 7, 8 an 9.

FIG. 11 shows a cros-sectional side view of the transducer with anelastomeric button covering the diaphragm of the transducer as anadditional coupling means.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference to FIG. 1 shows a blood pressure transducer or monitor element10 connected to a four-wire multi-conductor cable 12, comprising a rigidmetal surstrate 14 of generally rectangular plan-form having a widthapproximately that of the subject's finger or thumb. Substrate 14 has acontact face which fits to the inner surface of the finger or thumb ofsubject's right or left hand, as shown in FIGS. 7, 8, 9 and 10. As shownin FIGS. 3 and 4, a folded edge 16 runs the length of one side ofsubstrate 14.

"Velcro" strap 18, as shown in FIG. 1, is secured at one end thereof tothe edge of the substrate 14 by forcibly crimping the fold 16 over andon the respective end of strap 18 laid flat on the back face of thesubstrate, as shown in FIG. 2. From under the crimping edge 16, thestrap 18 passes over the back face of the substrate 14. Strap 18 isseparately wrapped around the subject's finger or thumb and thesubstrate 14 and these are secured together in a single assembly, asshown in FIG. 10. A wire clamp 24 mounts to one end of substrate 14 forholding the end of cable 12 and three of the four wires therefromoperationally connect to terminals 34-36 while the fourth wire groundsthe substrate 14, as shown in FIGS. 1 and 3.

Reference to FIG. 3 also shows a circular aperture 22 centrally locatedin and somewhat smaller in area than the contact face of the substrate14. As shown in FIG. 4, a circumferential shouldered relief 26 centerson the aperture 22 and cuts in the contoured contact face of thesubstrate 14. A thin, flat, circular diaphragm 27 of slightly smallerdiameter than the relief 26 rigidly mounts around itd circumferentialedge therein solidly up aginst a shoulder thereon havng the outer edgeof its contacting surface bearing a continuous generally flush relationin its central portion with the curved surface of the contoured face ofthe substrate 14. A diaphragm retention means 28 which in installed atthe juncture between the circumference of the back face of diaphragm 27and the cylindrical wall of the relief 26 retains the diaphragm 27therein and produces an essentially rigid relationship between thediaphragm 27 and the substrate 14.

Diaphragm 27 mounts in the substrate 14 in flush relation with thecontact face therewith so that, in mounting th transducer 10 on thesubject's thumb or finger, as shown in FIG. 4, the contact face bearsupon the surface of th subject's skin with an average pressure which isapproximately the same as that exerted on the subject's skin thereaboutby the contoured face of substrate 14. Subject's subcutaneous blooodpressure is then transmitted to the diaphragm 27 in an approximatelinear relation therewith, with subject's skin alone acting as thecoupling means, and proportional lateral strain from normal deflectiondue to subcutaneous blood pressure fluctuations threin is developedthereon.

A half-bridge circuit 38, as shown in FIG. 6, has two scaling resisors39 and 49 each in adjacent arms of said bridge. The bridge 38 alsoincorporates electrical wire strain gages 29 and 30 in the same adjacentarms which are bonded in proper central location on the back face of thediaphragm 27, as shown in dotted line in FIG. 3 and in solid line inFIG. 4. Half-bridge 38 measures the proportional resistance unbalancedue to the change in strain gages 29 and 30 on the back of diaphragm 27,and converts this strain to an electrical signal output therefrom whichis proportional to the subject's subcutaneous blood pressure fluctuationapplied to the monitor 10.

The monitor 10 has one lead 31 which electrically is in common with andconnected at one end to the first end of each of two strain gages 29 and30 in the adjacent arms of the bridge 38, as shown in FIGS. 3 and 6. Theelectrical terminal 34 connects to the other end of electrical lead 31.An electrical lead 32 connects at one end to the other end of the straingage 30 in one arm of the bridge 38. The scaling resistor 49 connects atone end to the other end of electrical lead 32. The electrical terminal36 connects to the other end of the resistor 49. An electrical lead 33connects at one end of the other end of the strain gage 29 in the otherarm of the bridge 38. The scaling resistor 39 connects at one end to theother end of electrical lead 33. The electrical terminal 35 connects tothe other end of the resistor 39. Terminals 34, 35 and 36 are eachbonded to the back face of the substrate 14.

The four-wire multi-conductor cable 12 has a first, second and thirdconductor 45, 46 and 47 each connected at one end to terminals 34, 35 ad36 respectively. A fourth conductor 48 as one end operationallyconnected to the fourth wire in cable 12 which grounds the back face ofsubstrate 14.

A four-prong plug-in connector 37 of the quick-disconnect type havingflat male terminals 50, 51, 52 and 53 pierced to accomodate solderwiring and spaced for standard plug-in mounting each of which issolder-connected to the other ends of first, second, third and fourthconductors 45, 46, 47 and 48 connects the monitor 10 to standard controland display modules to read-out and record the blood pressure in thesubject's finger or thumb.

A standard circuit 40 and automatic recorder 42, as shown in FIG. 5,completes the system.

In another version, as shown in FIG. 11, the diaphragm 27 is mounted inthe substrate 14 in flush relation with the contact face therewith sothat, in mounting trasducer 10 on the subject's wrist, the contact facetheron bears a uniformm contact pressure relation on the surface of theskin thereof for the full area of the substrate 14 and the convex sideof an elastomeric button 54 covers said diaphrgm 27. Button 54 has adiameter approximately equal to that of the diaphragm 27 and a thicknessof about one-third of its diameter. The flat side of the button 54 alsobears this same contact pressure relation on the surface of thediaphragm 27. Likewise, subject's subcutaneous blood pressure is thentransmitted to the diaphragm 27 in an essentially linear relationtherewith, with the button 54 acting as the coupling means in additionto that of the subject's skin and proportional lateral strain fromnormal deflection therein is developed therein is developed thereon.

In the installation of monitor 10 on the subjct's finger or thumb eitherwith or without the elastomeric coupling button, proper contact bearingpressure of the diaphragm 27 against the surface of the subject's skinfor proportional read-out of subcutaneous blood pressure is insured byuse of a contact bearing pressure adjust system 44, as shown in FIG. 10.The pressure adjust system 44 comprise a Velcro strap 18 which is woundaround the subject's finger or thumb and transversely over the back faceof the substrate 14 placed thereon for the case of using the dry skin asthe sole coupling means, as shown in FIGS. 7, 8, 9 and 10, and for thecase of using in addition the elastomeric button 54 as a coupling means,as shown in FIG. 11. The strap 18 is wound thereabout subject to adeterminable amount of tension according to the degree of tightnessdesired therein to give the desired contact bearing pressure of thediaphragm 27 against the surface of the subject's skin for essentiallylinear response of the monitor in recording subject's subcutaneous bloodpressure without occlusion of the free flow of blood in his vessels.

One specific use of this invention, although there are others, is in thefield of truth verification wherein the stress of emission of afalsehood causes the subcutaneous blood pressure to quickly change andbe noted on the monitor.

Although but one specific embodiment of this invention is herein shownand described, it will be understood that details of the constructionshown may be altered or omitted without departing from the spirit of theinvention as defined by the following claims.

We claim:
 1. A monitor of subcutaneous blood pressure comprising:a. abody having a contact face for bearing against the skin of a subject, aback face and an opening in said body extending from said contact faceto said back face; b. a diaphragm operatively mounted in said openingfor deflection of the same in a direction perpendicular thereto having acontact face in continuous and substantially flush relation with thecontact face of said body and having means for securing the edge of saiddiaphragm thereto with substantially a rigidly-mounted edge-fixity; c. ameans for operationally holding the contact faces of the body and thediaphragm therein at a determinable contact bearing pressure against theskin of the subject; d. an electrical strain-sensoroperatively-connected to an input source of electrical power mounted onthe back face of said diaphragm having an electrical output in directrelation to the strain input from the deflection of the diaphragm undersubcutaneous blood pressure; e. electrical bridge and amplifier circuitoperatively-connected to the electrical output from the strain-sensor;and f. pressure indicating and recording means operatively-connected tothe electrical output from the bridge and amplifier circuit.
 2. Amonitor of subcutaneous blood pressure, as set forth in claim 1, whereinthe strain-sensor comprises at least one electrical strain gage.
 3. Amonitor of subcutaneous blood pressure as set forth in claim 1, whereinmeans for operatively holding the contact face of the body and thediaphragm therein at a determinable contact bearing pressure against theskin of the subject comprises a tension strap overlapping the back faceof the body and including a fastening means secured on each of the endsthereof for fastening said strap at a determinable tension therein andhaving a determinable contact bearing pressure against the surface ofthe subject's skin.
 4. A monitor of subcutaneous blood pressure as setforth in claim 3, wherein the fastening means comprises anadjustable-length fastener.
 5. A monitor of subcutaneous blood pressureas set forth in claim 4, wherein the adjustable-length fastenercomprises a Velcro strap.
 6. A monitor of subcutaneous blood pressure,as set forth in claim 1, wherein the improvement comprises anelastomeric insertion having a convex shape on the side contacting thesubject's skin and a flat shape on the side contacting the diaphragm anda thickness approximately equal to one-third its diameter between thediaphragm and the subject's skin.
 7. A monitor of subcutaneous bloodpressure as set forth in claim 1, wherein means for securing saiddiaphragm to the aperture in said body comprises: a. a peripheralshoulder around the edge of said opening; andb. a retainer between saidshoulder and the peripheral edge of said diaphragm.